As described in the copending application, valves for use with vacuum equipment are essentially different from valves used in conventional systems whose objective is to control the flow of a liquid or gas. In such conventional systems, some leakage of the liquid or gas can usually be tolerated. In the case of vacuum valves, however, even the slightest leak involves not only the loss of a liquid or gas, but total destruction of the vacuum in the vacuum equipment controlled thereby. Therefore, no leakage can be tolerated in vacuum valves.
The valve of the present invention, like the valve of the copending application, is intended primarily for use as a vacuum valve in which even the smallest leaks cannot be tolerated. A positive sealing action is assured in the assembly of the present invention when the valve is closed, this being achieved by the use of a Teflon plug which engages a seat in the valve in a leak-free sealing relationship, as will be described. Like the valve of the copending application, the Teflon plug in the present instance is forced against the valve seat by the stem of the valve when the valve is closed. In addition, a compression spring engages the plug, so that the plug is held in its sealed condition, even in the presence of cold flow of the plastic material. In the valve of the present invention the Teflon plug is shaped to perform a scraping action on the seat when the valve is opened or closed to keep the seat free of debris.